Mr Abbott says the roads funding commitment would help to ease traffic congestion in Sydney, Melbourne and Brisbane.

He says $1.5 billion will go towards Melbourne's East West link to help ease traffic congestion.

There will also be $1.5 billion for Sydney's M4 East project, linking the CBD to west, and $1 billion for the Gateway Motorway in Brisbane.

"We will work with the states and the private sector to ensure that these projects have started to go ahead within 12 moths of the next federal election because the Australian people need to know that our great cities are no longer at risk of gridlock," he said.

"Our big cities are no less vital to our economy than our vast resource developments and can properly be considered part of our national economic infrastructure.

"Almost nothing signifies progress more than new roads."

New South Wales Roads Minister Duncan Gay says the M4 East project is long overdue and the money will help kick start work which is expected to cost up to $10 billion.

"Terrific news for the people of Sydney, and especially the people of the west," he said.

Mr Abbott says there will also be promises for a project in Adelaide and for the Bruce and Pacific Highways announced before the election.

The Opposition Leader has not specified where the money would come from, but it is understood it is likely to be from the existing Commonwealth road fund - the "roads to recovery program".

'Mythical promise'

But Ms Gillard says people cannot drive on an empty promise.

"Where is the $1.5 billion coming from? Did you get a fully costed sheet when Mr Abbott announced it?" she said.

"The answer to that is no. This is just a little mythical promise, $1.5 billion for a $5 billion project, and he can't tell you where one cent is coming from."

Mr Abbott also used his Melbourne address to again pledge to dismantle the carbon tax if he wins government.

He says the next election will be a referendum on the new tax.

"From tomorrow, every problem we face will get worse under the carbon tax," he said.

"Soon the Australian people will pass their judgment on this bad tax based on a lie. The next election will be a referendum on the carbon tax. It will be a referendum on prime ministers who tell lies.

"When I say during the campaign there will be no carbon tax under a government I lead, Australians can be 100 per cent certain that I am telling the truth."

Ms Gillard, who spent Saturday selling the carbon tax to voters in Melbourne's east, says it is an important reform at the right time.

Under the scheme the country's biggest polluters will be charged $23 for every tonne of emissions it produces.

Ms Gillard says millions of Australians will receive a tax cut as compensation for any cost of living increases.

"People will wake up tomorrow around the country and go about their normal Sunday. Doing what they do, catching up with family and friends, watching a bit of sport on TV, many people having to go to work," she said.

"But they will be in a position from tomorrow to judge for themselves the claims that have been made to see what carbon pricing really does mean, to see the change it means for a clean energy future and also to see for their household budget what tax cuts mean, what increased family payments mean and what pension increases mean."

It's a fundamental human yearning to be a part of something bigger than one's self, and maybe that's what drove my mate Ash to die, far from home, in a bloody foreign war against Islamic State, writes C August Elliott.